1. Field of the Invention
The present invention relates to a differential chopper comparator and an A/D converter including the same.
2. Description of Related Art
In recent years, high-speed and highly accurate A/D converter (Analog to Digital Converter) is used for video signal processing or the like. A differential chopper comparator is known as a comparator provided in this kind of the A/D converter. This differential chopper comparator is mostly composed of CMOS transistors, and is mounted to ASIC, for example.
An example of such differential chopper comparator is disclosed in Japanese Unexamined Patent Application Publication No. 5-206756. FIG. 4 is a part of FIG. 14 of Japanese Unexamined Patent Application Publication No. 5-206756. FIG. 5 illustrates control signals Φ11 and Φ13 supplied to the differential chopper comparator.
The configuration of the differential chopper comparator of a related art illustrated in FIG. 4 is described hereinafter. A switch SW11 is provided between an input terminal I11 supplied with an input signal voltage Vin and one end of a capacitor C11. Further, a switch SW12 is provided between an input terminal I12 supplied with a reference voltage Vref and one end of the capacitor C11. Switches SW13 and SW14 are provided in parallel between the input terminal I12 and one end of a capacitor C12. The capacitors C11 and C12 hold electrical charges when the input signal voltage Vin and the reference voltage Vref, which are respectively supplied to the capacitors C11 and C12, are connected to the capacitors C11 and C12. The capacitors C11 and C12 are referred to as sampling capacitors in this document.
Then, the other ends of the capacitors C11 and C12 are respectively connected to a positive phase input terminal and a negative phase input terminal of a differential amplification circuit 50. One end of the differential output of the differential amplification circuit 50 is connected to the other end of the capacitor C11 via the switch SW16. The other end of the differential output of the differential amplification circuit 50 is connected to the other end of the capacitor C12 via the switch SW17.
The control signal Φ11 controls the switches SW11, SW14, SW16, and SW17 to turn on and off. Further, the control signal Φ13 controls the switches SW12 and SW13 to turn on and off. As illustrated in FIG. 5, the control signals Φ1 and Φ13 have pulse widths of constant cycles, and the phases of the control signals Φ11 and Φ13 are opposite.
As described above, the differential chopper comparator of FIG. 4 is provided with the switches S11, S12, S16, and the switches S13, S14 and S17. The differential chopper comparator cancels out the influence of the switching noise (feedthrough) generated from the switches S11, S12, S13, S14, S16, and S17 at the time of switching between the sample operation (reset operation) and the hold operation (comparison operation).